According to the results of an international study, coil contraceptive devices might protect women against developing cervical cancer even though they don't stop the infection that commonly leads to the disease.
Cancer of the cervix is the second most common cancer in women across the world, with about 500,000 new cases and 250,000 deaths each year, according to the World Health Organization. Virtually all cervical cancer cases are linked to genital infection with HPV, which is the most common viral infection of the reproductive tract. Drug makers Merck and GlaxoSmithKline have vaccines that protect against HPV and many wealthy and some developing countries have started nationwide immunization programmes for girls to prevent more cases of cervical cancer.
While coils are unlikely to be recommended as way of preventing cervical cancer – the second most common form of cancer in women worldwide – the research should reassure women and their doctors that using them carries no added risk of the disease.
For the study, Spanish researchers looked at 20,000 women and found that those with a history of using coils, or intrauterine devices (IUDs), were no less likely than women who don't to contract the human papillomavirus (HPV) that causes cervical cancer, but they had only around half the risk of developing the cancer itself.
The scientists think possible explanations for the protective effect of coils could be that the process of inserting or removing them destroys pre-cancerous cells, or that it causes some kind of inflammation that prompts a long-lasting immune response and prevents the HPV from progressing.
“It was a little unexpected,” Xavier Castellsague of the cancer epidemiological research program at the Llobregat Hospital in Catalonia said. “The data (available) before we did this study were very inconsistent, so we didn't expect to find such a strong association with this protective effect.”
A coil is a plastic and copper or hormone-containing contraceptive device that is placed in the uterus to prevent sperm from joining with an egg.
Previous studies have shown that using coils can protect women against another type of cancer called endometrial cancer or cancer of the womb, but until now it was not clear whether they could also have an effect on the risk of cervical cancer.
Castellsague's team, whose study was published in the Lancet Oncology journal on Tuesday, analyzed data from 10 case-control studies of cervical cancer done in eight countries and 16 HPV prevalence surveys in women from four continents. The findings were adjusted for the number of sexual partners and other confounding factors.
The results show that coil use did not affect the risk of HPV infection, but was linked to a markedly lower risk of cervix cancer for both major types of the disease – reducing the likelihood of developing squamous-cell carcinoma by 44 percent and adenocarcinoma or adenosquamous carcinoma by 54 percent. The length of time that women used a coil did not significantly alter the risk, the researchers said.
They found the risk was reduced by nearly half in the first year of use and the protective effect remained significant even after 10 years. “IUDs are not inert devices,” Castellsague said. “Our speculation is that they act as a foreign body and stimulate inflammatory changes that prevent the HPV infection from persisting and progressing to more advanced stages.”
“The hypothesis is that an IUD, because it's a foreign body, creates an inflammatory response that gets rid of the HPV, which reduces the risk of cervical cancer,” agreed Dr. Howard Jones, chair of obstetrics and gynecology at Vanderbilt University School of Medicine.
“People have suggested in the past that having an IUD put people at increased risk for developing cancer, and we are not seeing that,” said Dr. Ira Horowitz, professor and director of gynecological oncology at the Winship Cancer Institute of Emory University in Atlanta.
Should women worried about cervical cancer ask a doctor about using an IUD to prevent cervical cancer? It's too soon for that, Dr. Carol Brown, a cervical cancer specialist at New York City's Memorial Sloan-Kettering Cancer Center, said. Dr. Brown, who wasn't involved in the new study, said the findings need to be confirmed with more rigorous trials. Only two percent of American women use IUDs, although the devices are more popular around the world.
“The protective effect of IUD use challenges some key elements in the current model of the natural history of cervical cancer,” wrote Dr. Karl Ulrich Petry of Klinikum Wolfsburg in Wolfsburg, Germany, in an accompanying comment.
“These data may be reassuring for women who have IUDs, but I don't there will be a substantial impact on prescribing them,” said Dr. Johnathan Lancaster, director of the Center for Women's Oncology at Moffitt Cancer Center in Tampa. IUDs are expensive and can cause complications, such as pain and heavier bleeding during menstruation, so doctors don't believe the benefits outweigh the risks. Barrier methods, such as condoms, are a better option for women who are more sexually active. “Condoms reduce the risk of both HPV infection and HIV infection,” said Jones.
Experts also say women using these devices should get regular Pap smears. “This does not mean that women who have IUDs should change their practice of cervical screening,” said Lancaster. Currently, screening guidelines recommend that women who are sexually active should have a Pap smear every year. Starting at age 30, women who have had three normal Pap tests may opt for screening every two to three years.
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